Building boards, manufacturing apparatus and prefoamed plastics

摘要

A building board comprising a cement substrate, a top coated layer formed on the front surface of the substrate, and a plastic sheet formed on the back surface of the substrate. The plastic sheet should preferably be formed of a polyethylene sheet. Since the impregnation of water from the back surface of building board can be effectively prevented, the change in dimension of board as a whole can be minimized.